Just found that mossburg makes a semi 930 set up for three gun that can be had for the same price as some of the new 870 express tactical models. Around $600. The 930 I used guiding in the fall didn't fail me once..... So now another gun is thrown in the mix. I'm not a big mossburg fan but for the money it's hard to beat.

It will probably come down to what I can get a hold of locally for the cheapest.

Benelli supernova tactical can be had for $500 plus or minus $100. Needs mag tube and side sattle
Remington 870 SGA or 870police or 870express tactical needs seem to be any where from $499-$799 depending on model. Needs side saddle.
Mossburg 930 three gun or 930tactical model semi auto. List $730-$780 but I hear they can be had for $100 cheaper. Needs side sattle